Heretofore, various HFA production methods are known and for example, Patent Documents 1 to 4 propose methods for isomerizing hexafluoropropylene oxide. Hexafluoropropylene oxide is known to be obtained by a method of oxidizing hexafluoropropene with oxygen, which is disadvantageous in that the oxidation yield is low and production cost is high.
In addition to this method, a method for oxidizing hexafluorothioacetone dimer is known (Patent Documents 5 to 8, etc.), which is disadvantageous in that the yield is low and purification is difficult. Moreover, a method for fluorinating hexachloroacetone by HF is known, which poses a problem in that purification is not easy (Patent Document 9).
In view of the above-described problems, attempts have been made to produce hexafluoroacetone using, as a starting material, a derivative of octafluoroisobutene, which is a by-product produced when hexafluoropropene is produced. For example, Patent Document 10 discloses a method for oxidizing octafluoroisobutyl methyl ether with oxygen in the presence of an activated carbon catalyst. However, the inventors of the present invention found by testing this method that hexafluoroacetone was temporarily obtained but the catalyst activity of activated carbon was noticeably degraded, and thus this method was not technically carried out. In addition, Patent Documents 11 to 14 disclose methods for producing hexafluoroacetone from a derivative of octafluoroisobutyl methyl ether, but all of the methods have a low yield, and none of them are suitable as a method for producing industrially hexafluoroacetone at low cost.
Non-patent Document 1 discloses decarboxylation of a salt of carboxylic acids by reacting it with fluorine gas in an aqueous solution. Such decarboxylation, however, does not proceed with chlorine gas.
[Patent Document 1] U.S. Pat. No. 3,321,515
[Patent Document 2] Japanese Unexamined Patent Publication No. 1978-25512
[Patent Document 3] Japanese Unexamined Patent Publication No. 1983-62130
[Patent Document 4] WO 03/008366
[Patent Document 5] U.S. Pat. No. 4,337,361
[Patent Document 6] U.S. Pat. No. 4,334,099
[Patent Document 7] Japanese Unexamined Patent Publication No. 1982-158736
[Patent Document 8] Japanese Unexamined Patent Publication No. 1982-203026
[Patent Document 9] Japanese Examined Patent Publication No. 1965-27173
[Patent Document 10] Japanese Unexamined Patent Publication No. 1989-203339
[Patent Document 11] Japanese Unexamined Patent Publication No. 1986-277645
[Patent Document 12] Japanese Unexamined Patent Publication No. 1989-26527
[Patent Document 13] Published Japanese Translation of PCT International Publication for Patent Application No. 1997-509425
[Patent Document 14] Japanese unexamined Patent Publication No. 2001-81056
[Non-patent Document 1] J. Org. Chem. 34, 2446 (1969)